Integrated circuits are manufactured by a general sequence of steps wherein photoresist is coated onto a substrate, the photoresist layer is patterned by exposure and development, the pattern is transferred to the substrate, and the photoresist removed. This sequence of steps is repeated to build up multiple layers of patterned circuitry. For the photoresist removal step, plasma ashing is commonly used since etched photoresist residues may be difficult or impossible to remove using only wet cleaning, especially without damaging other materials that are present.
Positive photoresist is soluble in alkaline aqueous solutions as well as in compositions consisting of select organic and inorganic compounds. However, photoresist that has been exposed to a gas-phase plasma etch, such as a gas-phase plasma etch used for etching dielectric materials, will typically develop a hardened crust or residue, on the surface. The residue typically consists of cross-linked organic polymers, and may contain small amounts of silicon, metal, and halogen or other atoms.
Damascene or dual damascene processes commonly utilize a plasma etch such as that described above. The plasma etch may be a fluorine-based plasma etch to etch silicate-based interlayer dielectric (ILD) materials. These materials may include silicates, organosilicates and fluorosilicates. Fluorine-based plasma etching may cause fluorination of the cross-linked organic polymers that form the residue described above. This fluorination typically increases chemical resistance. Thus, the residue becomes difficult, if not impossible, to remove by conventional wet stripping techniques. Ashing using an oxidative or reductive plasma can remove the residue. However, plasma ashing is prone to damage to the ILD materials, especially low-k ILD materials.
Therefore, a need exists for photoresist removal that can remove photoresist residue but does not damage the ILD materials.